Two users working with custom groups

Here is a question for savvy users as I can’t figure out this by myself.

My colleague and I have one database (call it Database A) with 70000+ records. Our task is to go through the database and categorize the referrences. Of course, not all will be categorized, only a few thousand out of 70000+. Since we both work independently, we each have a copy of Database A on our computers and we will not modify that database.

I have created a lot of Custom Groups (200+) into which we will be draging referrences (this is what we call categorization). However, since we are working independently, how can we sync our custom groups? I have noticed that only some of the files in rdb folder are updated when custom groups are modified but Database A is left intact without any alterations. Ultimately, we want to end up with Database A and with our combined Custom Groups that ‘slice and dice’ Database A.

My thinking is that Smart Groups are a separate file located in rdb which gets modified. But I have no idea as as to what csort.frm and misc.myd and misc.mid files do and what is their format.

I am open to any suggestions.

I am using EndNote X2.