Curious about how people use date lookups

Hello fellow Excel nerds.

For context I work in projects for a pension admin company in the UK and a lot of my work involves comparing system held data with excel calculated values to find discrepancies.

I'm using a tool built by a different team and I'm responsible for processing the data. The tool relies on data being entered into the system with the correct dates so when I export it the tool can automatically look up the historical values.

You probably won't be surprised to hear that there are discrepancies in the dates used. For a relatively small set of data it is easy enough to manually adjust the dates so that the look ups work and the macro can process them correctly but this will not always be the case so I'm curious if anyone has experienced a similar issue and how you would deal with this for a larger data set.

I have thoughts on how to do it but I'm always keen to learn so am interested in the communities thoughts on this.