USCIS processing dates

[SREVY]

USCIS processing chart is updated every 15th of the month. Now In USCIS webdite its mentioned as per sep 30th followed by the processing time nd if the delay in process the received date of the case which was last processed before updating the chart But what does that sep 30 mean?

Does it mean the information is with respect to sep 30th processed cases or

The processed case before updating the chart