Formula to lookup latest revision but data entered prior to current revision should not ch

I have two sheets:
1) Item database sheet: in this sheet , I maintain all information related to particular items viz. price,description, drawing no., drawing revision no. & revision applicable date etc.
Items are identified by their item codes
2) Po entry sheet:Here i enter po no. item code of item for which po is received, drawing revision mentioned in po etc. Based on the item code data is retreived from item database sheet.

Refer attached file for the layout of two types of sheets mentioned above.
For simplicity, I've removed irrelevant entries.I've also shown the output needed.

Drawings keep on revising.Therefore I've created multiple coloumns for revision data entry in item database sheet & their date of arrival.
Question is, that in PO entry sheet, based on item code, latest revision should be extracted onto the PO entry sheet revision coloumn AND the data which was extracted before the arrival of the new revision, should not be recalculated or disturbed. Old record should keep on maintainig the revision no. that was latest/valid on that particular date of po.