I was thinking maybe they changed sms standards and bumped up to 200 characters per message, after reading your post... But to my demise, nope. We are still at the 160 max, with some networks falling clear down to 70... of course those networks are nearly obsolete(in the USA anyways, I haven't checked elsewhere). I have several android devices... None of them have default keyboard apps, so I may not have the ability to check what you are looking for, due to the fact that it may be built into the keyboard app settings?. I have no messages settings in the settings area of my phones or tablets.
I am running 2.3.4 and above on all devices, so I am wondering if they changed something. and of course each manufacturer/provider has their own software that comes pre-loaded on he devices... andI don't have any LG products.
The only thing I could come to with my current experience with androids, is possibly after 200 characters the device converts to a mms message instead of sending two sms messages. although all of my phones have mms conversion after 160 characters, thus a multi-sms message gets changed over to mms before it even has the chance to post two sms messages instead.
Now if you are correct about it not having more than 200 messages per conversation, check the first message in the conversation, possibly it removes them as you go, but keeps a tally count? I'm just in a grasping at straws attempt here.
Hope someone has your answer?