RM -- (1) The Sub-Assembly Issue can usually be traced to deletion of some Feature that was used to Constrain things (just so as you know). (2) As defined under MIL-Q-9858 (Mil Std Project Management requirements), one is required to archive a Project's Development at least every 24 hours. My habit is to create a Package of my Project at any significant change (adding the designator of YYYYMMDD (where "YYYY" is the 4-digit year and "MM" is the 2-digit Month and "DD" is the 2-digit day) plus a letter ("A" for the first change of the day, "B" for the second change of the day. etc.) to make sure that it is clear as to which archive is which. It is cheap insurance!