They also spell out how our existing flights will be calculated towards lifetime status:
Recognition of Status Stars points to obtain Frequent Traveller Lifetime and Senator Lifetime:
Of course, we are aware that you have already been flying with us for some time. We will therefore convert the Status Stars points that you have accrued up until 31 December 2020 into qualifying points so you can obtain Frequent Traveller Lifetime or Senator Lifetime.
Conversion factor: two Status Stars points will be equivalent to one qualifying point. All frequent flyers with four or five Status Stars will thus be awarded Senator Lifetime at the beginning of 2021. You will receive Frequent Traveller Lifetime if you have already achieved three Status Stars by the end of 2020.
If this is correct they are just counting the number of days someone had status irrespective of whether this status was earned on LH group metal or on other airlines. This works very well for me, I will come out at over 8000 lifetime points under the new system.