Well how do they? for example laminta with gorget ? or gothic armor with a great helm?

depends on what you mean by 'interact'

Sometime stuff will work, sometimes it won't. It is dependent on the particular pieces. Some museums routinely display things that weren't meant to go together. And there are definitely folks in some re-enactment groups that wear stuff that doesn't go together (and occasionally they'll wonder out loud why something is uncomfortable...)

Arms, for example, some have a rolled upper edge on the upper cannon. With certain spaulder or pauldron styles this may not work. Or it may sit a little funny and still function fine.

Helmets tend to be swapable, because of the space at the neck (unless you start talking about the really crazy integrated gorgets/close helms of the later 16th C that attach to the breast and back plate, but if you have one of those, why in the world would you want to wear it with the wrong thing?)

But gauntlets and arm harness - the basic form of the vambrace and cuff (length does, shape to some extent - but the size of the cuff opening relative to the size of the wrist) don't really change all that much for a long time. So you could probably easily wear an 14th C hourglass gauntlet with a late 15th C gothic harness. Similarly for the late 15th C gothic gauntlet and late 14th C arm harness.

cuisses and greaves - if you take a set of 14th/15th C upper legs and try and wear them with say a greek greave w/integrated knee - you'll likely have some problems. Even a set of 14/15th C legs without greaves can feel heavier or more uncomfortable without greaves - hence why a number of surviving pieces have indications of integration into the upper leg (pins, strap loops, etc)

But it *will* look wrong to someone who knows whats what, and possibly to those that don't if you go real overboard.

Thank you for the info sir that was most informative :)

In antiquity, I am sure that there were many examples of this happening; either because of munition-grade items stocked in armouries, battlefield pickups, heirloom/inherited items, or even older items that might have be gotten at a 'good deal'. I'd actually be suprised if this was not a somewhat frequent occurance in the lower rank and file - to have items of mixed manufacture/era due to any of the above reasons.

It would be interesting to see the strangest or most-mismatched assembalage of armor on display somewhere that was actually historically worn as it is now displayed. :D

When the fortress at Rhodes fell in 1522 to Turkish besiegers they seemingly had little interest in the armour the Hospitalers had on hand as alot of it was left sitting there until it was broken up and auctioned off in the 19th and early 20th centuries. Thom Richardsson and Chip Karcheski tracked down as many of thes items as possible and assembled them in " The Armour from Medieval Rhodes " a few years back. One of the things I found interesting was that there were armets and breast plates from the 1430's still on hand and in use. These peices were nearly 100 years old at the time of the fall of the fortress and still in service. The rest of the armour spanned from the 1430's right up to the fall of the fortress so a wide array of different aged armour was seeminly being combined to equip the troops there.

The rich and powerful would want the newest kit in the most recent style if only for " prestige " reasons and I could only see one of these rich and powerful use some older or mismatched armour bits if they lost their primary equipment and had to improvise with local stuff found in an armoury if caught in a siege and have not other available sources of top of the line armour.

At the same time a mercenary force made up of peasants, poor knights or a city militias might not care past the usability of the armour even if old and mismatched, and even more so during a revolt or siege or other emergency arming of non-full time warriors ?

There are bad matches due to function and fit and bad matches because it is offensive to the eye ! It might be offensive to the eyes in period or just to our modern sense of historical neatness.

Say, a spangenhelm mixed in with gothic plate and a kite shield using a rapier as the main weapon! Sounds fairly ugly to me and unlikely, but a bascinet 75 years out of date with gothic armour ?

I'm not saying that the old armor would have been thrown out--only that I strongly doubt that pieces from one end of the date range would have been fitted to others from the opposite end. So, while I can easily see the Knights at Rhodes outfitting a man in a combination of 1430s and, say, 1460s or 1470s kit, I don't think they would have matched, say, a 1430s armet with a 1520s cuirass; if nothing else, I doubt such a combination would have been able to sit comfortably on the wearer.