I believe the TSX-V stated position is an ending value. The shortdata information provides volume during the related period. To me, it appears the value we're missing that would provide the continuity is the number of short trades that were covered within the same period of time.

If these same information sources would simply provide full disclosure we would be able to comprehend better but from my perspective it is:

Opening short position: 18,000 (TSX-V)

Short traded volume:560,255 (Shortdata)

Short volume covered:560,217 (assumed)

Ending short position: 18,038 (TSX-V)