Ok, this is likely a measurement problem. To get a true, 700ppm increase in salt would require 187lbs of salt added to a 32,000 gallon pool. This is not a chemical issue. This is a measurement issue.
Is the pool store using a drop-based titration test? Unlikely, they usually use strips. Strips are highly unreliable and often have an error of +/-400ppm when brand new. They age and they go bad very easily.
Digital testers are electrical conductivity meters essentially reading TDS. Unless the tester is specifically calibrated with a known standard sodium chloride solution or standard TDS solution, they can easily lose calibration. Also, an electronic meter is going to detect ALL forms of conductive ion species including the calcium ions in your pool. So unless you have accurate and independent measures of all other components of the TDS, teasing out the salt concentration is exceedingly difficult.
You need to get a Taylor K-1766 salt test kit. It measures chloride ions (Cl-) directly and is an EXACT test. There are no interferences from other ions. It has a standard +/-200ppm tolerance for a 10mL water sample but can also be made more precise simply by testing a larger volume of water (a 25mL sample has a +/-80ppm tolerance). This is the ONLY test that I recommend for salt level measurements. Everything else is a proxy test that measures "something else" and infers the salt level from there. Even your SWGs do not accurately measure salt levels.
Do yourself a favor and ditch all the other tests and purchase a K-1766. It's roughly $25 and you'll get 50 to 100 tests out of it before any of the reagents expire; that's more tests than you ever really need.