Most of the potential confusions arising from name changes in Stace 3rd edition are listed in this MapMate Newsletter -
http://www.mapmate.co.uk/newsletters/102. But Sagina is not mentioned.
There are a suspiciously high number of records for Sagina apetala for date class 1987 - 1999 cf post 1999, and I suggest that anything recorded as Sagina apetala (without subspecies) before Stace 3 should probably be referred to the s.l. taxon, which is an option available in the DDb. Records could be bulk edited with an explanation as to why the edit was made. From a quick look at vcs I know, it looks looks like the issue is widespread, but VCRs would need to carefully investigate records for their vcs.
As this may be a general problem, it may be best for Tom to deal with it. Kevin Walker mentioned to me a few days ago that he and Tom were identifying 'problem' taxa such as this.