The 2020 session of the General Court was interrupted by the coronavirus pandemic and the full legislature did not meet from mid-March until mid-June. Normally, late March/early April is when bills "crossover" - move from one chamber to the other - but many bills never made it through. (A bill must be passed in identical form by both chambers of the legislature before it can become law). Only 39 chapter laws were enacted in the 2020 session (as compared to 346 in the 2019 session) but many of the individual bills that stalled because of the shutdown were consolidated by the Senate into "omnibus" bills at the end of the session. Omnibus bills aren't new but it is unusual to have so many that include such diverse topics in one bill.
To compile a legislative history for a 2020 omnibus bill, you will need to look at the omnibus bill and the original bill if any. (In some situations, the Senate added new language that didn't originate in another bill.) The source note in the RSA will lead you to the omnibus bill, but not to the original bill. Read the committee files and legislative journals carefully. Often, one of these will say where the language originated. If not, a bill text search for similar language will turn up the original bill. When the 2020 legislative journals are available (as of the date of this post, they probably won't be available for several years), use the subject index to find bills on similar topics.
We can expect to see more omnibus bills from the Senate in the 2021 legislative session. The Senate has appointed a Select Committee of Four with instructions to review and recommend the consolidation of similar legislation. The purpose of this special committee is to combine similar bills and to reduce the number of public hearings during the COVID-19 pandemic. It is planned that the Select Committee will operate for the first session only. For more information, refer to the Senate Journal, Dec. 2, 2020.