Any increases in allowances which are based upon service rendered prior to the applicable date of this article (as fixed pursuant to Section 31874) shall be funded insofar as possible from the moneys in the reserve described in Section 31592 which are in excess of one (1) percent of the assets of the retirement system; except that in counties which have applied Section 31592.2 the board of supervisors may fund all or part of the increases from the county general fund.