The SEC has issued a Securities Act Release that provides guidance on Rule 144. One frequently asked question answered by the release is whether there are any restrictions on securities sold in reliance on Rule 144. In the SEC's view, a purchaser in a Rule 144 transaction receives unrestricted securities. No action has been taken on those proposals. If a purchaser of restricted securities in a private placement can get a registration covenant from the issuer, as soon as the issuer files a registration with SEC covering the restricted securities, the purchaser can resell without restriction anytime during the effectiveness of the registration statement.
Special rules govern resales of securities in a variety of other situations.