... I'm just trying to familiarize myself with the differences between the older Lionel Corp and the new Lionel corp. ...
Simple premise... But the answer could get long and complicated. Probably best to search the forum, since I'm sure there have been some very thorough answers related to Lionel's history in prior threads.
Bottom line... The "old Lionel Corporation" that many of us 50-something and 60-something fellows grew up with stopped producing trains in 1969. So that was when folks stopped refering to Lionel as the "Lionel Corporation" -- except for today's Standard Gauge tinplate trains that MTH produces by licensing the Lionel name for its Lionel Corporation Tinplate (LCT) brand of trains.
For much of the 1970's and 1980's, Lionel O-Gauge trains were made my General Mills' MPC division with the Lionel name/brand on it. Product boxes were often white /red. Arguably not Lionel's finest chapter, but MPC kept the trains in our hands until Richard Kuhn took the reigns into the 1990's, transitioning us out of the MPC era (thankfully) and into the LTI era for several years. I think the LTI era is when I can recall the product boxes making a return to the post-war style orange/blue colors.
During all of this time, Lionel trains were primarily made in the USA except for a brief -- and poorly executed -- attempt to move production to Mexico. Mike Wolf had developed production relationships in Korea back then, and helped produce a few notable projects for Lionel, like the Reading and Chessie T-1's of the late 1980's/early 1990's-timeframe. But it's not generally accurate to say that MTH made O-Gauge trains for Lionel, except for a few years when Lionel offered Standard Gauge tinplate trains under the brand Lionel Classics in red boxes. Today MTH licenses use of the Lionel name to produce its Lionel Corporation Tinplate brand of tinplate trains. Aside from that, MTH and Lionel O-Gauge products remain distinct and separate product lines.
As for the numbering scheme, the 6-dash numbers have been around since the Lionel MPC days. I can't recall ever seeing that with the trains I grew up with in the 1960's.
I'm sure others will chime in with lots more details -- if they haven't already while I've been typing this post.
David