I don't know this for sure, but my impression is that the Flex cabs, once released, didn't get tweaked the way some of Mike's other cabs did. I recall the following versions:
- 110 Flex.
- 210 Flex (single cab). I'm not aware of any tweaks to this one (at least not anything major). I think it stayed pretty much the same since it was released.
- 210 Flex Mod(ular) -- a 1x10 top with the mid drivers and tweeters plus a 110 sub. Together, these were functionally the same as the 210 Flex (single cab -- a modular 210 Flex).
I think that the 110 Flex (which I believe could also be run with the sub) was distinct from the 210 Flex Mod top cab (which could also be run stand-alone) in that the 210 top cab had two tweeters (which could be run both on/both off/one on) rather than one (which you can see in @spiritbass's photo, a few posts up) and that the crossover/switching options might have been a little more involved and/or optimized for use with a sub with the 210 top.
Aside from that, I think they stayed pretty much the same, though I am aware of Mike doing a few mods by request for a few people (including me), as follows:
- Some guy in a really loud band wanted a 310 Flex Mod (top and two subs, I think). I remember Mike talking about it and I believe that, in addition to adding another 110 cab, the crossover might have been tweaked accordingly.
- For my 210 Flex Mod and at least one other (mine was not the first), Mike modified the crossover and added a switch so that, when running the top cab solo, the sound would be a little thicker than otherwise.
- For my cab, just before I sold it, Mike mentioned wanting to try different 6.5" mid drivers in it -- he thought the result would be a little smoother and more balanced overall. I thought the stock drivers sounded great, but he seemed to think these would be an upgrade, yet. I told him to go ahead with it -- he wasn't charging me for the upgrade and wanted to satisfy his own curiosity -- and he did report liking the result even better than the stock configuration, but I never got to hear it with the new drivers: the cab sold and shipped direct from Mike before I could try it. If Mike tried these drivers in another Flex cab, I am unaware of it.
Again, I could be wrong -- there might well have been substantive revisions to the Flex cabs that I don't know about -- but I don't think so. (If folks are aware of examples of such, please share.)
I ended up keeping my MAS 112 -- I dug it and it was a more practical cab for me at the time -- but the Flex was probably the best "I don't need a PA" cab I've played, not just in the sense of being able to get loud (lots of cabs can get loud), but how full and good it sounded out in the house and how even and audible it was on stage and in the house without needing to blow out the stage. (That said, a 210 Flex is not a small space, low volume cab, IMO, though the top/110 on its own might manage that -- @spiritbass could speak to that better than I!)
EDIT: One could always ask Mike. If you do, feel free to point him to this post (and please follow up here if you learn anything of interest).