It would be great if Zabbix will support some custom field in the item configuration, which can be used then in requests (HTTP agent, some other item types, including Zabbix agent). Such field value would be used to know next request start point. For example, when request some events from other systems, the field can remember last known processed "eventid" / "clock". After receive new data, the field must be updated according received data.

The field is more less similar to internal field related to eventid for VMware events processing, but with possible configuration using web-interface. It is possible to store such value in item_rtdata, then using macro reuse in "HTTP agent" requests, for example, special JSON output / preprocessing can help with post-processing:

[
{ "value" : "....",
 "objectid" : "10" },
{ "value" : "....",
 "objectid" : "20" },
{ "value" : "....",
 "objectid" : "30" },
]