sounds like you could have had an air bubble or something in the lines. When it got dislodged you had the spongy breaks. A couple pumps replaced the lines w/ fluid, but then your fluid was low b/c the air had been removed.
Also, as your breaks wear down you fluid level goes down too (to make up for the difference lost at the pads). If you are very concerned then you should bleed the lines and replace all the old fluid. Else just filler 'er up.