I seem to recall that if two BSAs contained the same resource files (meshes and textures) there could be problems, but I can't remember the details?
Could it explain why NPCs given clothes and arrmour from the CNRP mods look fine if the files are not BSA'ed, but some meshes or textures show up as invisible if in a BSA, if the same resources are also contained in the OOO BSA?
In other words, it may be best to only pack non-conflicting files into a BSA?

There have been reports of conflicting assets in BSAs leading to crashes, but I don't recall the details or have a link to the thread that got discusses in. Aside from that, H2Odk did a lot of research into this and if he sees this thread he can probably comment.

I have made some test with BSAs, and they showed that they have priority based on name. But this seams to indicate there might be more to it. Could you provide the names of the CNRP mods, and the armors/clothes?

Unfortunately the problems I had was with my my previous game, but I was reminded about the fact since I'm now in the process of BSA'ing the largest of my installed mods. So far I've installed all my mods without BSAs so that I have full control of meshes and textures conflicting, and I noticed the conflicts between OOO and CNRP in BAIN.
But I'll BSA the CNRP mods and try again, either today or tomorrow. OOO is not currently BSA'ed so it will be interesting to see if the NPCs edited by CNRP show up with missing body parts this time.

In general I would only recommend BSAing unique files.

I even made a recommendation in the Wrye Bash thread that it should unpack any conflicts from a BSA (and redate the BSA to 2006) to ensure that the game use the correct files based on install order.

If packed in a BSA, does a (texture or mesh) file's date have any relevance?

Just checking I'm repackaging my pyffied meshes correctly, thanks

I did a little test run with all the CNRP mods BSA'ed and this time I saw no missing body parts. Incidentally there weren't that many conflicts with OOO, nearly all the conflicts are with the other CNRP mods.
It's possible that packing the files with TES4Files and using the "fix nifs" option did the trick for me this time.

No, only the date (and name) of the BSA has relevance. (I actually don't think that the date is stored in the BSA.)

I don't think so either, every BSA I've ever unpacked the files get creation dates at the time I unpack them.