If you crank through population numbers as given in Y2 against known deaths, the population is always a bit high, supporting the argument for births. I've chatted with David Welle about this and he has done exhaustive statistical studies based on known canon facts coupled with extrapolated population breakdowns:
www.space1999.net/metaforms/kb/s19kb2h.htm#pop2v
www.space1999.net/metaforms/kb/s19kb2h.htm#poplysum
The takeaway point... there are little Alphans out there somewhere.
(Information from David's Metaforms website Knowledgebase.)