Well...

By first strike, the major TPG's are assuming that by being first release coins, they were the very early ones made on the dies. It is a rather large assumption on their part. To be more accurate, the TPG's should name the early coins 'First Release' rather than First Strikes, because how do they know? They don't. They are simply stating that the particular coin labeled first strikes was recieved by them within the first 30 calendar days of the release of the coin. This prevents coins being made a month from now (which no doubt they will be) from being under the First Strike label.