I agree with Luis on this. If you VIP a tank with a hydro due in less than 12 months, date the VIP sticker so that it "expires" the same month the hydro expires. This would be to prevent the tank being filled in the event the fill station operator reads the VIP sticker but fails to note the far more important hydro test date.
The definition of when the VIP expires is however where it gets interesting.
The standard used to be pretty much universal that the VIP expires at the end of the month, just like the hydro test (ie: a hydro test date stamp of 05A04 expires May 31 2009 and the matching VIP sticker would be punched May 2008 to expire May 31 2009.
However at some point some subset of inspectors, trainers and agencies decided that if the VIP were done on May 1 2008, the user might get 13 months between inspections and that this would somehow be wrong or dangerous so they dictate that the VIP expires on the first of the month - or in this case May 1, 2009 rather than May 31, 2009.
Personally I think the first of the month view is pretty stupid as it conflicts with the DOT regs regarding hydro test dates. Scuba industry standards aside, a VIP is a required part of the hydro test so any different interpretation get the two out of sync from the start with a 5 month discrepency developing between hydro tests. That benefits no one except the dive shop selling 6 VIPs per 5 year period rather than 5. Practically speaking if properly inspected, either 12 or 13 months is frequent enough to catch any developing problems. Anything that poses a threat with a 1 month extension will be something obvious like an odor to the gas or water sloshing inside the tank.
From a regulatory perspective federal law trumps any state or lesser laws or regs so if push came to shove, the first VIP on a freshly hydro tested/requalified tank would expire at the end of the month 12 months after the test was completed. ie: a 05@08 hydro and VIP would require a new scuba industry mandated VIP on the first day following May 31 2009 in other words, June 1 2009.
But it is one of those areas where common sense left the building a long time ago and the LDS doing the fill petty much has the customer over a barrel if they decide they won't fill a tank with a VIP sticker that was punched in this same month the preceding year.