The DPDD tells us that "Level 1 data products are a result of difference image analysis" (§3.1), as opposed to "Level 2 data products [which] result from direct image analysis" (§4.1).
However, this definition is incorrect. Per LSE-29 (which is the highest-level document in which I can find this defined), "Level 1 Data Products [are] the result of processing of the stream of image data from the Data Collection system during the course of normal observing" (LSR-REQ-0033), while "Level 2 Data Products [are] the result of periodic processing of the entire archive of raw image data from the Data Collection system" (LSR-REQ-0036).
This isn't just mindless pedantry: I think there's an important distinction to be made here. A literal reading of the DPDD would suggest that level some 1 data products are generated during an annual data release, while some of the products of nightly processing (e.g. PVIs) are actually level 2. That's inconsistent with usage elsewhere, and I find it actively confusing. Can we fix it, please?