When a static blockage occurs, it affects not just the altimeter and VSI, but also the airspeed indicator. If the static port blockage has happened on the ground, the air pressure that was ambient at the time the static became blocked is what ram air will be compared against during the takeoff. If lower pressure is trapped in the back end, or in other words, in the static end of the instrument, then the airspeed will read higher.
In this particular case, because of the combination of blockages and the way the system was plumbed, we didn't see uniform errors that immediately pointed to the entire system, or necessarily to the alternate static as a relief.
During the takeoff roll, normally the pilot not flying would set power, make airspeed calls, etc. The pilot flying might glance at the airspeed (which the captain did), but I didn't make any calls. I had been monitoring my airspeed, but last saw it much lower than the rotation speed. I was busy trying to do everything during the takeoff, including the fine setting of the propellers via the electric step-head motors (something not found on the original airplane, incidentally). When the captain called "Rotate!", it was then that I noted my airspeed was too low. My initial thought was that I'd failed to make the call. I hadn't. The captain rotated early, and with a nose-high attitude and considerably more drag, the airplane took a lot longer in the takeoff roll. It was when he realized that the airplane wasn't going flying, apparently the tail skid already having contacted the runway, that he abruptly brought the nose back down and got my full attention.
There was no way to reject the takeoff at that point. The airplane came with fairly weak, expander-tube brakes that would quickly fade with heat, and had no reverse. Dumping the retardant would have had the effect of coating the brakes and runway with slick retardant and making stopping impossible. Going was the only option, and we went, albeit with some confusion in indications and with the trees in our way. I think it was mostly the gear that went through the trees, rather than the whole airplane; no damage from the trees was observed.
The event underscores another principle that should be followed (but wasn't, that day); knowing where on the runway you can safely reject, and where you should be off the ground. A good habit, even (and especially) in light airplanes, is knowing the runway and having features or points along the runway in mind where you'll either reject if you're not off, or where you'll expect to be getting airborne. This serves as an additional safety tool.
I always made a habit in light airplanes of walking the runway before taking off, if I could. Obviously at a busy metro airport, this wasn't always possible. But at runways where the takeoff really would become critical, such as rough dirt or gravel or grass runways in tight canyons or other short field events, I always made a habit of pacing the runway off and inspecting it as I went. This would include making a note of where I expected to be airborne or where I could reject and get stopped. It might be as simple as noting it would by that pile of rocks or by this bush...but having a good concept of what to expect during the takeoff, and a way to measure the performance in addition to staring at the airspeed indicator, is always a good idea.
The airplane I'm flying presently uses up a great deal of the runway. In my original groundschool for this airplane, the instructor liked to say "If you don't like seeing red lights during the takeoff, you won't like flying here." I was used to seeing the red lights during the takeoff roll, so wasn't overly shocked at the frequency with which we are in them, and we do very much abide the takeoff speeds...but we're flying a "numbers" airplane. Many light airplanes are flown as much by feel as by numbers, and rightfully so. The 4Y, likewise, was flown by feel much of the time rather than by numbers, though we always respected the numbers...and as you can see, an early rotation had dire consequences in takeoff performance. A proper analysis at the time would have included the observation that although the airspeed was indicating high enough to rotate, perhaps the ground speed looked inadequate, and perhaps it as too soon on the runway.
The airplane in question was of WWII vintage, and had fairly limited performance charts. They were the original WWII charts, in fact, as was the flight manual, general and armament manual, mx manual, etc. With a recent frontal passage, a change in air pressure, and a headwind, and limited takeoff performance date beyond experience and some elementary calculations, the captain used his best judgment (which turn out to be that great, it would seem). He could be forgiven for seeing the airspeed rise more quickly than anticipated, given the headwind, and at the time, the altimeter difference seemed a fairly insignificant issue given the mission. My altimeter reflected field elevation when set to the altimeter setting, and the conversation was simple, along the lines of "yours is correct, we'll use yours."
This brings up another note, which is that we had dual altimeters; one for each side. Many light airplanes, especially single engine airplanes, have only one airspeed indicator, one altimeter and one VSI. Discrepancies may not be as easy to note. Thus it may be that the VSI that's off slightly may be the only initial indication of a bigger problem, or the altimeter that won't quite set right.
Another takeoff in an other place in the 4Y began normally, with all normal airspeed indications, but toward the latter part of the roll, as we rotated, the speed bled back and began to decrease. There was no stopping at that point, and we had a low overcast. As we entered it the speed finally bled back to zero in the climb. We flew pitch, and power. We attempted to correct with alternate static, but to no practical avail. This reaction is typical of a static blockage, where airspeed tends to bleed off as altitude increases. Once we were up and stable, rather than attempting to turn around in a mountainous area and go back and land, we got safe, and I went below and forward, where I was able to break static line connections and eventually restore instrumentation. This isn't something that's usually possible, or advisable, in a light airplane.
At the destination, we removed all the pitot and static line segments, as well as the pitots, and blew them all out into filters. We found water and several insects in various points, which had provided variable blockages. The blockages leaked air and weren't consistent, and didn't add up to an obvious cause as it was happening. That event illustrated the wisdom of not worrying too much about the "why" so much as simply flying the airplane.