DVD-R cannot be re-written at all.
You are not saving money by not buying RAM discs, you are losing money by turning your "r" discs into coasters. If what you have said was to be the case, then there would be no need for DVD-RW. RAM is the only re-write format for Panasonic. I have the E50, and you can delete before formatting on -R, but as kenfowler has rightly stated, you are only preventing the "deleted" recording from being shown......and the time on the disc is not recoverable.