Check it by hovering over won/sent CV numbers on your SG profile. Not SGtools.

One difference is that there may be a delay when SGtools sync bundle/no-CV list. So real CV can be higher there.

Another is that SGtools treats no-CV games differently, for the purpose of real won CV calculation. SG counts won no-CV games as bundled (from what I remember), but SGtools doesn't count them at all. And we follow SG statistics for group calculations.

Years ago we only had RawCV shown on SG, and then level progress. To make it easier for people to follow level / CV etc., knsys added the won / real CV calculation. But then when the admin added those stats directly to SG, and decided to count all won GAs towards CV (as a truer indication of how lucky someone is, otherwise you could win dozens of games and have 0 real CV in won) - knsys did not adjust their calculation. Values for ratio calculation of won/sent are taken directly from SG, but not the actual values displayed to users that you linked to. Here is one post I managed to find that touches on it:

https://www.steamgifts.com/discussion/b736C/tool-sgtools-new-section-deals/search?page=39#OBftLWI

Edit: I made a mistake. It's not that no-CV GAs are counted as bundled. It's about "less than 5 entries". So this GA counts as a won bundled CV for you according to SG, but not SGtools:

https://www.steamgifts.com/giveaway/5M8ku/marooners

It's the same with all won GAs with low entry number.