Listing and trading are different
A bond can be listed on an exchange without trading frequently. Finding its ISIN in a directory does not establish the quantity currently available or the price at which you can transact.
Put a date next to every price
A historical trade records a transaction that happened. An indicative valuation is an estimate. An executable quote is an offer to transact subject to its terms. These are different kinds of evidence, and each needs a timestamp.
Think about an early exit
If you need to sell before maturity, the available price may be affected by market conditions and buyer demand. Check recent trading activity, available quantities and transaction costs. A historical price does not guarantee the same exit price today.
Before buying, ask your platform how selling works and what information it provides on recent trades and available buyers.