DMcG,
I cannot believe you do not see that if they have different regulations the situation is different.

The criminals who supply illegal foodstuff do not adhere to regulations.
They had no problem moving the stuff through EU soft internal borders.
That is not how they were uncovered.

If we keep a soft border, there is no difference.
If EU imposes a hard border, it will still make no difference because the border posts will not carry out checks on the actual food, just the paperwork.

The border is utterly irrelevant to that crime.