320 (7B) 10 y ban calculation

[psw2008]

Dear experts,

I have an issue, which I researched pretty well. However, I still see some black spots.

The case: a person applied for a Tier 1 PSW leave to remain from inside the UK in Sep. 2008. In the application he mistakenly made a false representation by answering negatively to the question if he had a civil court judgments against him (in fact, he had a small debt recovery judgment in his home country in 2004). He wasn't challenged over this, got his permit and several times within the leave period left and re-entered the UK with the last departure in Aug 2010.

Now, he plans to file a visitor visa application soon. Despite the fact that the probability of discovering this civil court ruling against him is relatively low (due to various technical issues), he is willing to state it in his instant application (without any mentioning of the previous omission, of course) so that not to drag this risk with him for another 10 years.

My thoughts:

1) If an ECO discovers this, he will be obliged to refuse the instant application under 320 (7B) as deception was used in an earlier application (with no regard to being caught (320 (7A)) or not, material or not).
2) The 10-year ban period has not expired yet despite the application was filed in Sep 2008 as the person applied from inside the UK and the last departure from the UK under the permit applied for with deception was in Aug 2010 (acc. to the General grounds for refusal guidance). Am I correct by stating that the last voluntary departure will be taken into account in this case and not the first one to calculate the ban time?

Are there any defects in this logic? What may be the best strategy to do in this case? Is it better to wait until Sep 2020 to fully avoid any chance of discovery (all the relevant UK entries will be outside a 10-year disclosure period by then)?