OK. Just got back from a swim - had knee surgery recently and things seem to be coming along, well, swimmingly. Was thinking a bit more about military language and started drifting back into the Roman imperial era, and Latin epitaphs in particular. Now, it's been a while since I've read anything about an inscription beyond some papers/chapters/books that use them for the material they contain, rather than as something to be evaluated as an end itself. Thus, what I'm about to say may in fact be bollocks - someone or more likely some ones have probably discussed this somewhere. I'll have to take a look.
Anyway, if my memory serves me, and it may not, as you from the early first century (AD) to the late second century (AD) the abbreviations, at least with respect to those epitaphs that honour deceased military men, tend to become more pronounced. Granted, some other more standard abbreviations emerge while others disappear, but if we're talking about those used for military units and titles I think they become shorter and shorter. If this is true, why might they have done this? Well, it could be for economic reasons. Tombstones became more affordable, so more people wanted them. In turn, to churn out an increased number of stones those producing them might have had to cut corners - minimize time by using shorter and shorter epitaphs with more and more abbreviations.
What I'm wondering, however, if there's any correlation between an increase in the use of abbreviations and the findspot of epitaph of a soldier. If more and more soldiers were being buried where they were based (and I do believe soldiers were less and less likely to go back home after their term of duty came to an end) then the need to spell out the units they served in might have been minimized. In other words, with epitaphs found in environments filled with soldiers, this target audience may not have felt the need for the names of military units to be spelled out. They're could read and understand the abbreviations, just like my friends could understand each other. So, a possible hint at military language and its prevalence in military environments.
As I type this, however, I realize a lot more work would be needed before any such idea went futher than this. I'd have to do some reading. I'd have to look closely at not just the military inscriptions from a region (the whole empire might be unrealistic), but all of them, their findspots, and so forth. And, if there is an increasing number of abbreviations used in the Roman period over time in general and in a variety of contexts (that is not more likely in a military environment - i.e., they're used everywhere) then the theory goes out the window. Still, when I start looking a bit more closely at inscriptions again, hopefully in the not too-too-distant future, I might give it some more thought.