I recently acquired some model trains of different brands some are Bachmann, but there Tycos, Athearn and a Reverra (Not sure on the spelling of the last one).  I think they may have been made in the 70's but I'm not sure.  So my question is how do you date model trains?  I think I see a month and year on the side of some and others it looks like it may be on the bottom.  They are all HO scale or gauge, still learning the difference, and would like any feed back anyone may have.  I may be looking at selling some of them and would like to have a little more information.  I do have two boys so we might keep them and have some fun.  A couple are still wrapped and look new and never used.  Do the 70's era, if they are from that era, have some collector value?  Any help would be greatly appreciated.