When and how did you create the feeds?
When you first post data to a feed that is when it is created and thus, it’s the start time for the feed, if you later try and post earlier data, it will not accept data timestamped any earlier than that feed start time.
If you were (for example) to create the inputs, processing and feeds, then post data that was a year old, you could then at any time post further data that was more recent and as long as you always move forward in time you should be ok. You cannot “backfill” data to feeds.
Try replacing the feeds with new ones and use only the oldest data.
Also try using absolute time stamps within the data and &time=0 as anything else might skew the timestamps (see Best way to guarantee times when using BULK load with PHPTIMESERIES? - #2 by pb66)