A complex problem-replacing repetitive numbers with blank

Dear All, once again thanks for reading and trying to help. Its one of the most wonderful forums I have been to!
I'm attaching a mini replica of the excel file I have. As you will see, there are company names in the first row and company codes below each name. Its a time series daily data for 30 years. Now, here is the problem. For some companies (those which say 'dead' after the company name-for example column F company, ABN Granites), after a certain date (in the case of ABN granites, its 17-02-1997) the values are repeated till the end (again in the case of ABN granites, that value is 5.56 which starts at around the same date-17 feb 1997). There are few other companies in this file which are dead and have the same issues after a certain date.
In the original sheet-and I have many such sheets-, there are approx 200+ companies which either have the word, dead or the word, susp, which has the same issue. Is there a way I can tell excel to replace all such numbers after a particular date with a blank? Manually doing it one by one will take hours if not days!
Please let me know if you want more information on this problem.
Thanks very much!