To level-set: I am an experienced excel + pivot table user, not a beginner.
Something strange is happening to my pivot table that I've not seen before.

I have created one pivot table and "date reported" is the row field of the
pivot table. The input data is mm/dd/yyyy hh:mm:ss AM and formatted
mm/dd/yyyy.
I am using other page and column fields like a normal pivot table.
Everything is fine ... date sorts correct as expected. Graph looks great.

I then right-clicked the tab and copied to a new tab ... to make a different
underlying pivot table so as to create a different graph

I did this about 10 times. 1 data tab, 10 pivot tables, 10 charts.
[Yes - the spreadsheet is huge: now 30 mb]

By the way, the date-reported field is grouped differently on the 10 pivot
tables.
[year-month; days-7; days-14 ... each pivot table is different]

Now the date-reported on some of the pivot tables is sorting as if it was a
text field. ex: 01/02/07, 01/03/06. Strangely, some pivot tables have
changed to a different date format. ex: 14-Mar, 21,-Mar.

I have tried to change the format and it won't budge.
I have tried to sort manual, ascending, descending ... it won't budge.

Is my spreadsheet just too big?

Any ideas?

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Thanks for your reply & assistance.
Jimbo213