There is no "passmark" for Tiffin schools - unlike the Sutton grammars. They simply offer places based on your rank score.
The highest standardised score is 280 - 140 for each of the VR and NVR test - but you don't have to get a particular mark to be seen as "of selective ability". The school will offer places to the top 140 boys based on their score (120 girls).
The lowest mark offered for entry on initial allocation is generally around the same score each year - give or take a couple of marks. So for girls it usually ranges from 233-237 with the boys about 8 marks or so lower. There are lots of threads on here to see how low the offer score has gone via the waiting list. Presumably if Tiffins ever adopts the practice of scheduling the test before the CAF has to be in , they too will introduce a passmark so you will know if your child has "passed" the test - i.e. reached the required standard to be seen as selective, but you still won't know if they have been offered a place until 01 March.
Hope that's clear