To further detail the situation I would direct you here:
http://www.atf.gov/firearms/faq/nati...#receiver-sale

Even though the weapon's serial number may still be on the NFRTR, it is no longer an SBR. The ATF has stated that there is no duty to notify the NFA Branch to remove the item from the registry when the item no longer meets the definition of SBR. All that is necessary to effect this condition is to have the barrel removed or replaced with a non-NFA length and the short barrel no longer being under the current owner's control. So...

Assuming that the item was an SBR when the PD had it, when they removed the short barrel and sold the receiver to you without a barrel, it was no longer an SBR. And they did not have a requirement to notify NFA Branch. It would be nice if they did, but they have no legal obligation to do so and not doing so doesn't mean that you have an SBR; you don't. Now, confusion could happen in the future if the weapon is used in a crime and the status comes up as SBS. You would have to show that the weapon was sold/possessed in a non-NFA condition. You could ask the PD if they notified ATF. If they didn't, take a picture of the gun with a long barrel/no barrel (and a clear shot of the serial number) and send that in with a copy of the bill of sale to NFA Branch notifying them that the weapon is no longer in SBR configuration.