I have a VG10 blade that I used to scrape some extra stubborn adhesive off some countertops in combination with some 409 cleaner...I would have normally used a putty knife but I'd left it with a co-worker at another jobsite so I conscripted my Spyderco for the job.
To my surprise, upon opening my blade the next day there were dozens of little rust spots on both faces. I used some chrome polish and they were erased without issue. I guess it was the bleach component in the cleaner I used

...but still I was surprised that VG10-- the "Japanese Gardener's steel"-- was affected in such a way.
Did you use your blade around some sort of household cleaner/chemical, perhaps?