The IMPORTRANGE() function occupies a range based on the data that queries. If you add some content within the datarange that importrange returns, the latter will break because it can’t expand.
You can either restrict the range that importrange occupies:
=IMPORTRANGE("SprdID";"All Months!$A$1:$D14")
or add content starting from column E. You can also put the importrange function in bottom rows and use the top rows for manually entered data.
Since the raw data could potentially increase in the future, I would advice you to have a dedicated sheet to accommodate the importrange function and all of the other calculations/formulas to be stored in a different sheet.
References:
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solved Write in the row under the function IMPORTRANGE