The 13 week period (1Q) is the typical lead time necessary for manufacturing electronics.I didn't mean early as in before the others, but at the same time as the others. When Intel releases new CPUs, OEMs (such as Dell, Acer, HP etc) will immediately release new products utilizing those products, which means they have gotten CPU shipments before the release date in order to manufacture the products. At least this is the case with consumer parts, I don't know is it much different with servers.
Basically, I was questioning your statement that it takes at least 13 weeks after the release of the new CPUs before Apple can release the new Mac Pros.
The ability to ship products on or near the same date as the official release of the CPU's used, depends on whether or not the vendor (whomever the case may be), was able to get chips before that date (~13 weeks ahead of the official date).
Some are able to do this when they buy directly from Intel, as it's centered around the volumes of what CPU are purchased. If the volume is high enough, Intel is more willing to make concessions (early shipments, lower pricing, ...).
Smaller vendors have to wait for the official dates, as they don't buy enough to get them directly from Intel. So they have to buy through Distributor channels instead (buy in quantities under 1k units, aka lots <1 lot = 1k parts>).