It's been a while but ...
I believe the systems will look for not just one or two common entries (First/Last Name) but for quite a number. I remember, years ago, that our system looked for a telephone number (even with slight mismatched names) as being a critical element. (We were flight firming, in the days when duplicate bookings were much more prevalent).
Since a home-printed boarding card is usually just a pdf file anyone with Acrobat Pro or lots of cheap / freeware alternatives can change the name to match the id that they have - no need for similar/same names to accomplish this. But as mentioned the airlines systems shouldn't let a duplicate sequence number board. Such efforts will only get someone through security and ...
There are other ways to do this it that's the goal - simply walk up to the ticket desk, buy the most expensive (refundable) ticket for any flight. Get a boarding card, go through security and there you are. Apparently journalists have been doing this for years so they can pounce on their subjects at the gate. Once their pouncing is over - they tell the airline they have changed their mind and get a full refund.