Yes. Each game is compatible with the latest rules, except for Guderian's Blitzkrieg (1st Edition). There may be some changes in terminology however (e.g. trainbusting).
Thanks a lot but I have just realised that I posted this on the wrong forum. I wanted to post it on the MMP one, because I was asking about several systems (SCS, TCS and GTS in addition to OCS). If you know the answer by any chance, please enlighten me.