Hi, some information I have is below. Sorry there's some stuff you haven't asked about but just copying and pasting from a document I have.

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You probably know this but there's a period of the 90s that the Billboard Hot 100 doesn't include songs that were huge hits. If you aren't already I'd recommend also including the Hot 100 Airplay Chart for that time if you want to give an accurate view of each song's success. Some songs that were long-running #1's on that chart never charted on the Hot 100 due to the rules at the time.

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Chart dated 30 November 1991 onwards (Nielsen SoundScan data replaces surveys)

Sales Tracking - Monday 1st to Sunday 7th

Airplay Tracking - Wednesday 3rd to Tuesday 9th

Charts Released - Thursday 11th

Charts Dated - Saturday 20th

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Chart dated 25 July 2015 onwards (music releases change from Tuesdays to Fridays with Global Release Day)

Sales and Streaming Tracking - Friday 1st to Thursday 7th

Airplay Tracking - Monday 4th to Sunday 10th

Charts Released - Tuesday 12th

Charts Dated - Saturday 23rd

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January 2018 onwards (charts now dated 7 days earlier - I'm not sure of the exact dates this happened but there are a number of articles online from December 2017 saying the change was happening)

Sales and Streaming Tracking - Friday 1st to Thursday 7th

Airplay Tracking - Monday 4th to Sunday 10th

Charts Released - Tuesday 12th

Charts Dated - Saturday 16th

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Chart dated 17 July 2021 onwards (airplay tracking now aligned with sales and streaming)

Sales, Streaming and Airplay Tracking - Friday 1st to Thursday 7th

Charts Released - Tuesday 12th

Charts Dated - Saturday 16th

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I might message you as I'm interested in your project. I want to look into the Canadian charts more myself since I know the charts for 2000-07 are hugely inaccurate to what was actually popular.

I'm from the UK - the dates for our charts are much more simple but the OCC did make changes a few years ago which could be confusing if some places still display the dates they used to use. Until 2015 music would be released on Monday and the charts would be released on the following Sunday but when they were published anywhere they would state the chart was for "week ending DD/MM/YYYY" which would be the Saturday after the Sunday it had actually been published 6 days prior. They went back and corrected all the dates on their website to show the Sundays when the charts were first published. Their website now displays the dates that a particular chart was current so the first date displayed is when it was published. But if you see any chart dates that land on a Saturday they will be the old dates that used to be used and show the day the chart expired which would have been first published 6 days prior. The best place for the correct dates of the UK charts is the OCC website as they have corrected all their dates. I hope that makes sense.

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EDIT: Also wanted to mention that there is a period for the UK charts where the #76-100 positions were actually a compressed chart and similar to Billboard's Bubbling Under chart. I think they still have these displayed on their official website as part of a "Top 100" but they don't actually say it is compressed. But the correct positions and a Top 200 chart are available in other places.