CYA Test Results

The tftestkits uses Taylor reagents so that’s not a problem.
The cya test is the one the pool stores get wrong more than right so that’s the likely reason for the difference.
Be sure u are doing the test outdoors on a sunny day with your back to the sun Proper lighting is important & can impact the results u see. The pool store does the tests indoors with artificial lighting.
You can pour the solution back into the squirty bottle, shake & preform the last part of the test multiple times to get an average/ feel confident in your interpretation of the results. If it reads between two lines, round up. Aka 1/2 way between 40 & 50 counts as 50.
If u wish to have a better understanding of the results u see you can get the standard solution to compare.

If you think the CYA is 50ppm, based on your test, go with it. Because you do your OWN testing, you can see if the SWCG is struggling to keep up with production based on high UV, high bather loads, etc.

I think that's a nuance of self-testing that is sometimes lost. Accuracy is important, but not the end all, be all. Self testing allows you to get to "know" your pool.