most recently completed representative period of one year
(1) The most recently completed representative period of one year ( 551.2(c)) or most recent representative annual period ( 551.5(b)(3)) shall mean a one-year period within which such employees were so employed on a regular full-time basis by such employer (or, if such employer has not previously used such plan, by another employer using the plan under substantially the same conditions, which period shall include a calendar or fiscal quarter-year ending not more than four months prior to the date as of which the effect of such plan is to be considered, together with the three quarter-year periods immediately preceding such recently completed quarter-year; and