InfoPath Dev

I have pulled data in from Access and created a SharePoint list. I would like to add items to the list and continue the numbering from the TA numbers that were in access but just adding 1 for each new item in the list. I know I can add more lines in the list and SharePoint would create an ID for me but it wouldn't match the numbers that are already there. I would like to be able to do this with the InfoPath form SharePoint created for me but I have not been able to figure out how to get it done. Is the form SharePoint created too limited?

Right before the form submits, you could query the list, get the max TA number and add one to it. The concern is that you need to do this right before you submit, or you could end up with two forms with the same number - say you do this on open, and the highest TA number right now is 10. Joe opens the form, and on open is assigned number 11. But before Joe submits, Sally opens the form. She also is assigned 11....

Thanks for the reply. That makes sense. Would I get the max TA with a data source or with a look-up field on the form?  In the datasource I only see a way to query the whole list. And if it is a look-up field I don't know how to do it right before saving back to the list.