Except that in the pedigree show they commonly name the son or they name the son & heir, in the case of Rici GRENVILE they state Sans Dat.
Dates are not commonly shown on that pedigree (or other similar pedigrees displayed) and where shown are added in a note, so why state make mention there that there was no date?
I still think they are saying he had no son, but I have no information on that family and cannot confirm whether he had a son at that time or only daughters, there is a Sir Thomas Grenville shown but without seeing more information on the family cannot say how he is connected.
That is why I framed my answer as I did.
Cheers
Guy
PS by at that time I mean Rici GRENVILE the named son may have died or perhaps may not be a legitimate son.