I can't see all historical data for the crypto pair, although it was traded before

We have data from multiple crypto exchanges and different exchanges have data starting from various points in time. If you do not need data from the particular exchange, please try to search for identical crypto pairs, but from different exchanges.

For example, historical data for ZRXBTC from Coinbase exchange is only available from Oct. 12, 2018. But in Symbol Search you can find the same pair from several exchanges:

When the same symbol, but from Binance exchange is used, historical data from Sep. 13, 2017 is available: