Aaahhh....yes....POHs.... or the lack thereof.
The biggest shamble I've been involved with in this respect was an FTO where, due to rapid expansion, they had been buying up various aircraft left and right, without bothering a lot about fleet commonality. After a while instructing on the Cessnas, I was due to be checked out on the Arrow, so that I could instruct for the CPL syllabus as well. I had about 80 hours on the Arrow III by then, so I wasn't expecting to find a lot of new stuff, but I still studied the SOPs diligently. The POH itself wasn't provided as the school wrote OMs with type specific SOPs that 'should' cover everything.
The checkout with the CFI in the other seat went well, but I was surprised a bit by the, to me, strange glide speed that I had to use in the relevant exercises. Then again, my experience was on fairly new Arrow IIIs, this was an older Arrow III and I was well aware that there could be some differences. It wasn't until I asked the CFI some questions about this after the flight that I realised the situation: they were operating both PA28R-200s (the Arrow II with the old slab wing) and PA28R-201s (the Arrow III with the tapered wing) using the exact same speeds and procedures from the Arrow II books. I ended up loaning my own general Arrow III POH to the CFI so he could read up and copy the relevant bits.... Within a few weeks the OMs and SOPs were adapted, but they still expected students to go from one subtype to the other without any fuss.
To keep things interesting, they also had a few PA28RT-201Ts (T-tailed and turbocharged Arrow IVs) but fortunately had realised that these were different and needed different procedures from the low-tailed non-turbocharged variants... Oh well. The interior fit and equipment was different for each individual aircraft anyway, so standardisation was a complete joke. I'm happy to say that the outfit isn't in business anymore (at least, under the old name...)