Integrity in Android data collection

Hi,

I have acquired Android internal using dd utility many times and noticed hashes are different in subsequent collection from same device with reboot(due to rooting process) in between. The reason was device clock changes and some sqlite file has been overwritten which caused changes in header values.

I haven't experience in data collection via recovery image. Though I have read collection through recovery preserve integrity in every subsequent collection process. Is this true? Is this way of collection independent of device clock changes as in the above case? As clock is running I imagine there couldn't have same hash values for data collection on same device at two subsequent instances.

Thank you,
indi