It's always struck me that the VB already contains one class that shows two sets of numbers - The DIVERSITY (DV) IMMIGRANT CATEGORY.
One set of rank numbers (analogous to the PD for EB) relates to cases that are Current for the VB month and can be approved. The second set of numbers forewarns DV applicants of the rank number that will be Current in the following month's VB.
What might be pertinent is that (due to the time constraints associated with the DV category), those with a number less than shown for the following month are able to file their I-485 in advance of actually becoming Current. For example, if their rank number was lower than shown in the January VB as becoming Current in the February VB, they could file the I-485 from January 1 onwards, even though it could not be approved until at least February 1.
I wondered where that system had come from. I haven't been able to find it in either the INA or 8CFR (although it's quite possible I simply did not look in the correct place or missed it). If anyone knows of a reference, I would be grateful for the citation.
What I did come across was this 2013 USCIS Memo outlining the procedure. Here's an extract:
This advance notification therefore provides an opportunity for adjustment of status applicants to file their Form I-485 applications earlier than would otherwise be possible, thereby enabling USCIS to begin review of such applications. This in turn affords USCIS additional time to determine an applicant’s eligibility for adjustment of status before the end of the fiscal year.
If indeed this system is implemented solely by USCIS Policy Memo with the cooperation of DOS regarding the VB, then it seems entirely possible that such a system could be set up for the EB category. The existing Cut Off Date would remain and a second date would be added where applicants could file an I-485 in advance, but could not be approved until they were current under the "real" COD.
The real advantage of this approach is that it complies with the current regulation at 8CFR 245.1 (g)(1).
(1) Availability of immigrant visas under section 245.
An alien is ineligible for the benefits of section 245 of the Act unless an immigrant visa is immediately available to him or her at the time the application is filed. If the applicant is a preference alien, the current Department of State Bureau of Consular Affairs Visa Bulletin will be consulted to determine whether an immigrant visa is immediately available. A preference immigrant visa is considered available for accepting and processing if the applicant has a priority date on the waiting list which is earlier than the date shown in the Bulletin (or the Bulletin shows that numbers for visa applicants in her or her category are current).
The other huge advantage is that it creates a disconnect between cases that can be a approved and those that can be filed. Under the current system, the single Cut Off Date both allows new filings AND approvals within the COD. This creates a very difficult balancing act for the Visa Office to ensure approvable demand does not outstrip remaining visas.
Advance filing would allow a much greater understanding for DOS of upcoming demand from USCIS. It has advantages for practically everybody either in, or administering the system (perhaps other than initial USCIS workload).
In normal practice, maybe the intention would be to move the "second date" forward incrementally, as with the DV rank number. That wouldn't rule out actually allowing everybody to advance file by setting this "second date" as Current for a short initial period (or even permanently).
I throw out the above as a potential discussion point and in the hope that someone else can better research how the existing DV Lottery system evolved in the VB. I have a nagging doubt that if it were that easy, it would have happened before.
As a PS, Pre Registration in the form USCIS has always put forward in proposed rule making agenda would be much more similar to the current CP system and would not have allowed filing of an I-485 at that time. Instead it would have been a two step process, with a pre registration packet being filed in advance of the PD being current under the COD. The actual I-485 would still have only been filed once the Cod was current