Wrx cvt/front diff leak fluid contamination

I took my Wrx to get all my fluids changed 5 months ago and I noticed a small leak near the cvt housing they drained the diff replaced the seal and put dye in the cvt to check for leaks my question is, how likely is it for shops to recycle old fluids when inspecting drivetrains and is it safe, they never specified if they used old or new fluid when filling and I’m just curious on if it would effect the longevity of my transmission/front differential