TC50 Transformer curiosity build question

I noticed that the (Demeter) transformer on my TC50 is held together with only two nuts/bolts (one on each side, mid-way up). typically they're held together with 4 nuts/bolts. in fact, on the transformer in question i can actually see the four holes in each corner where the bolts would normally go. i know mine isn't a one-off as i've seen pics of others that were assembled the same way w/only two nut/bolts. mesa isn't one that's known for cost-cutting measures so i'm just curious why this was done this way. any ideas from you techs out there?

The nuts and bolts are only used to secure the metal cover plates on the transformer. Laminations are generally pressed together and may be welded in some cases (depends on transformer manufacturer). It does not matter if a pair of screws or 4 screws are used. Cover may even be glued on as well but requires additional securing with screws or other hardware (depends on its construction, the "E" laminations may be general purpose and depending on the stack-up of laminations and the bobbin size there may be some builds using the same "E" core that has all 4 or 6 holes used with nuts and screws. I doubt there is any relevance to the performance of the transformer.