Liming 2 year covered soil before planting spuds?

[Two_Sheds]

Early spuds are usually lifted before scab has time to get established anyway.

My earlies get scab. They all do, unless I grow them in leafmould or MPC.

Limey soil doesn't by itself cause scab, but it provides ideal conditions for the thing that does.
POTATO SCAB- symptoms, cause and treatment

[Chef_uk]

Done the test today using a probe that i found in my dad's belongings. At first I wasn't sure if it was working as the needle stayed at 7pH on most of the soil, the level it shows at when not in use. I then probed the layer of homemade compost that i've put down as a mulch on a couple of beds and it lowered the read out to 6.5pH albeit slowly like a thermo probe does so does that seem right (that homemade compost would be lower than the soil)?