Verify if record has been posted to database before posting

I have written a macro to post a record to a database but want to check if the record is already in the database before I post the record? I have attached a sample file.
Thanks in advance

I have made an attempt at the code but besides being inelegant, it does not work?
Sub PostWeek()

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Thanks in advance

I am receiving an error message "Object variable not set" for the "IF Selection" line of code? Would really appreciate some guidance.
Thanks in advance

I have tried some different code but still can't figure this out? The logic I am trying to apply is that if the weeknumber has been posted, a vlookup will result in a positive number and if the week has not been posted, the vlookup will result in #NA.

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Thanks in advance

I have attached a sample file with new code that has a problem with the Vlookup line?
Thanks in advance

Is there an easy answer to this problem? I am hoping so.
Thanks in advance

Thank you very much. Works perfectly. I added the following code at to de-select the range:

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