That is not accurate.
Once that paperwork is approved, your firearm is a registered sbr. If you chose not to proceed, your firearm still is a nfa item and must be treated as such.
apples and oranges
You are missing the point that we are discussing converting a rifle to an SBR. You have a tangible, already manufactured item. It does instantaneously become an SBR. This is why it has become common practice to engrave before receiving back your stamp. If you have your stamp in one hand, and an unengraved lower with a matching serial number in the other hand you ARE illegal. Once the paperwork has been filed, you own an SBR regardless of what anyone else tells you. The SBR status follows the registered receiver and couldn't care less what configuration your rifle is in, be it a 5" .223 or 28" 6.5Grendel.
Section 6.8 Withdrawal or Cancellation of an ATF Form 1 and Refund of Making Tax. The Form
1 applicant may withdraw the application by submitting a request, in writing, to the Chief, NFA Branch.
The applicant may also cancel an approved Form 1 application by submitting a request, in writing, to the
Chief, NFA Branch. The request for cancellation must state that the firearm was not made and must
include the approved Form 1 with the stamp affixed. The NFA Branch will amend the NFRTR to reflect
the withdrawal or cancellation of the application and arrange for the refund of the making tax. A request
for cancellation may only be done if the firearm has not already been manufactured. If the firearm is
made, the tax liability is incurred and the applicant cannot seek a cancellation.
Q: I possess a properly registered SBR or SBS. I intend to strip the receiver and remove the barrel prior to selling the receiver. Is the bare receiver still subject to regulation under the NFA as a SBR or SBS? A stripped receiver without a barrel does not meet the definition of a SBR or SBS under the NFA. Although the previously registered firearm would remain registered unless the possessor notified the NFA Branch of the change, there is no provision in statute or regulation requiring registration of a firearm without a barrel because its physical characteristics would make it only a GCA “firearm” pursuant to 18 U.S.C. § 921(a)(3)(B). If the subsequent owner buys the receiver as a GCA firearm and installs a barrel less than 16 inches in length (SBR) or 18 inches in length (SBS), the firearm would be subject to a $200 making tax and registration under the NFA by the manufacturer or maker of the SBR or SBS. Because registration depends upon the stated intent of the applicant, there is no provision to allow registration of a NFA firearm by anyone other than the maker or manufacturer.
Q: If I remove the short barrel from the registered SBR or SBS, is the receiver still subject to NFA transfer and possession regulations?
If the possessor retains control over the barrel or other parts required to assemble the SBR or SBS, the firearm would still be subject to NFA transfer and possession regulations. ATF recommends contacting State law enforcement officials to ensure compliance with state and local law.
Q: Does the installation of a barrel over 16 inches in length (SBR) or 18 inches in length (SBS) remove the firearm from the purview of the NFA? If so, is this considered a permanent change? Installation of a barrel greater than 16 inches in length (SBR) or 18 inches in length (SBS) will remove the firearm from the purview of the NFA provided the registrant does not maintain control over the parts necessary to reconfigure the firearm as a SBR or SBS.
From the NFA Handbook regarding Withdraw and Cancellation of a Form 1
AS for a receiver being a SBR it is only one with a barrel of 16" attached to it and nor shorter barrels available.
From the ATF FAQ on SBR and SBS
ATF Online - Firearms - Frequently Asked Questions - National Firearms Act (NFA) - Short Barreled Rifles and Shotguns
Hmm...so if I am reading that correctly, I can take my lower previously registered as a Sbr, slap on a 16" upper and dance across any state lines I choose, without notifying anyone?
I swear they make this ***** up as they go.....