Based on what I am reading, you are not entitled to 6.9SP5. You would only be entitled to the version that was current at the time of your AUP expiration.
If I am reading your post wrong and you re-established AUP for 310 clients, under the current version you would only be entitled to 310 client nodes in DS. The remaining 50 clients from the old AUP could only technically be used on the version that was current at the time of the AUP expiration.
Expanding on that (assuming my second paragraph above is true), you would only install the current license file and not the previous licenses.
Hope that helps. Let me know if I need to expand on that anymore or if you have more information that could help me clarify it more.