When does the effective date for TRA '86 fall? Also, can someone provide an official source for this, perhaps a chart
When does the required effective date for retirement plans for TRA '86 fall? Can someone please provide an official source for this, with perhaps a chart describing when which provisions of TRA '86 have their own respective required effective date.

Also, can someone articulate the distinction between an effective date and an execution date?

I'll take the easy part . . .

Execution date = date document is signed
Effective date = date from which provisions control or are enforceable with respect to the agreement/document

There were many effective dates covering many years.

The TRA was a very complex act that had many different effective dates (perhaps hundreds). For example, non profit and government employers could not establish a 401k plan after June 2, 1986, salary reduction contributions to 403b and 401k plans were reduced to $7500 beginning Jan 1, 1987, new nondiscrimination rules were applicable for plan years beginining in 1989, etc. For each provision you need to research the effective date in the section of TRA 86 that made the change.