"Too much" was in reference to ZDP and we don't use that stuff in anything any more.
We now use ZDDP (zinc dialkyldithiophosphate = ZDDP) which chemically combines that evil phosphorous so it isn't running loose to attack grain boundaries.
And if you look at the amounts, the phosphorous is always less than the zinc because that is the way the molecule is built.
And if the old ZDP loose phosphorous available in the powder mix had to get all the way up to 2000 ppm, we don't ever get that high these days anyway and our phosphorous isn't loose anyway, it is locked into the zinc in a dialkyldithiophosphate molecule.
Read the SAE reference I gave to ART, it goes into it in more detail.
http://papers.sae.org/2007-01-1990/If you are still worried about it, pour in half from the old mixed bottle and half from the virgin bottle into the sump of your bike at next oil change, making a mix that is what you are going to go to next anyway.
Using a quart of each, you will have enough to do you two sump loads in that fashion.
Me, I'm going to stick with 2 ounces per gallon jug, or one ounce per sump. That's around 1459 ppm which is up a bit initially, but is OK to me as when I go to add some oil later due to use it will come on down accordingly.
Remember, I don't premix my jugs, I dope the sump loads separately as I like to KNOW it is all ratio'd out correctly at the time the sump gets hot that first time.
The thought of all the goodie being settled to the bottom of the jug after a year of sitting, well that doesn't sit well with me.