Secondly, for the overall argument of whether or not a lack of a statement at the time of Harry and Meghan’s wedding means anything, we should actually look at how the royal family works. LPs typically aren’t issued for people who aren’t conceived yet. The LPs for the Cambridge children were issued when Kate was pregnant with George. The LPs for the then-Edinburgh children (who would have otherwise been styled as the children of a Duke) were not issued until the then Princess Elizabeth was pregnant with Charles. Going further back, Princesses Alexandra and Louise of Fife were teenagers before their grandfather issued LPs to make the royals, and the three eldest children of the then-Duke of York (later George V) were all born before Queen Victoria issued LPs elevating them to HRH status.
In all likelihood, the BRF found no reason to issue any statement as for the time, any children born to Harry and Meghan will have the titles of the children of a Duke - there’s no need to issue a statement saying that children that aren’t conceived yet are going to have the style that they’re already intended to have based on the current LPs, nor is there any reason to expect LPs to be issued to elevate them at this point, as again no child is conceived yet.
If it is the intention that the Queen will elevate any future Sussex children, it is fair to expect the LPs will be issued during Meghan’s first pregnancy - just based on the precedent set during Kate’s first pregnancy and the Queen’s first pregnancy. At the same time, if it is the intention that any future Sussex children will not be elevated to the HRH title/styling when Charles is King, I would likewise expect such a statement during (or shortly after) Meghan’s first pregnancy - just so that it’s established before Charles becomes king. If, on the other hand, some course of events happen wherein Harry and Meghan don’t have children until Charles is king, then no LPs would be needed, but again I don’t think any statement about “downgrading” the children would be made until Meghan is pregnant. Ditto in the event that something happens to Charles before he becomes King, I think any LPs elevating future Sussex children would still not be issued until they’re at least conceived (with either the Queen elevating them or William doing so when he becomes king).