Sage 200 2023 R1 DLLs .Net 4.5

[Nigel Bogle]

This is a request for ADVICE please.  I am attempting to build an Integration interface between Sage 200 Professional On Premise 2023 R.1 and a C# Solution containing more than 50 projects developed in .Net 4.5 and .Net 4.6.1.
For a long and complicated reason which I can't really go in to here, we just cannot upgrade these existing projects to .Net 4.7.2 which is the current .Net version for Sage 200 2023 R1 dlls.
We obviously can't use .Net 4.7.2 dlls in a .Net 4.5 / 4.6.1 solution because it just won't compile.
We are asking if you have any suggestions please? 
We are considering using older Sage dll versions that were created under .Net 4.5 or lower or maybe 4.6.1. 
We are asking if you could inform us if there are any such dlls available, where we could get them from and most importantly if they would work against an existing implementation of Sage 200 2023 R1 and if there would be any adverse results in doing this.
Thank you in anticipation. 

[Geoff Turner]

The last Sage 200 version on 4.5.2 was (I think) 2021r1  (20.0.43.0).  You can reference these assemblies (with Specific Version false), which are still on the Sage 200 Developers Downloads page (https://my.sage.co.uk/UK/communities/developers/developer-centres/sage-200/sage-200-product-downloads.aspx)

But don't deploy them - use  whatever version the client has installed, using the documented method (https://my.sage.co.uk/Sage200SDKDocs/html/DOC0704_Overview.html) to resolve them.

As Sage have kept the AssemblyVersion of the client assemblies at 19.0.0.0, your product will then work with more-or-less any version of Sage 200.

PS. How weird that we can't put hyperlinks in this editor!