Metropolitan line now 'immunised' ???

I remember a thread a while back that was about a 1973 stock at Harrow-on-the-Hill and people were asking wether it could go further along on the Met or not and the answer given was no as it was not immune and would mess up the signalling, somthing to do with the static coverters or somthing?

Now that the S stock is cleared everywhere on the Met, does this mean it is immunised? If so can a 73ts run further than Harrow-on-the-Hill?

Thanks