Start with two single-chat files
Use a WhatsApp text export without media and a Telegram Desktop single-chat JSON export. Open Group Chat Awards twice, once for each file. In each tab check the first and last date in the file and the period selected in the tool. Leave any full-account export out.
Write down the actual window
Make two rows on paper with the app, first day, last day and message count for the same selected period. If the first available WhatsApp day is March 8, call that row “March onward”. An ambiguous 04/05 date needs a known message to confirm the order.
Handle the handover week
When both apps ran during the same week, mark the overlap. Keep the totals separate if you cannot identify repeated messages. For adjacent, nonoverlapping periods you may add the two counts as exported messages, with a note about any missing days.
Use a caption that tells the truth
For example, “Our first chat covered March–June; the second covered July–November. December is still open.” Keep participant names private and share only a card the group has approved. Try the synthetic sample to see the layout before selecting a real file.
Worksheet to copy
App | First date in export | Last date | Period counted | Messages in that period | Missing or overlapping days