I can't figure out if this is just someone that is super sadly confused or an inept attempt at malicious market manipulation.
Needless to say there is no fire here.
Files like "blk00000.dat" are not the blocks by themselves. They are files that get filled with many blocks written as you download them. In early software (pre 0.8 IIRC) they would grow to 2GB (maximum vfat file size) before moving to the next one. The constant appending for a single large file created disk fragmentation and isn't very compatible with pruning, so later versions make smaller files and pre-allocate their space.
The format of bitcoin's database files has changed over time for performance and stability reasons, and so some newer versions convert older files to new versions when you upgrade. The release notes for versions note when a database rewrite is required, and upgrading to those versions usually takes a long time as it converts all the files.
The blocks themselves can never be changed once they are created, unless the software wasn't really bitcoin but was really some other network (like the BCash chains that some scammers try to pass off as "Bitcoin"). But if you had malicious software it would do whatever malicious thing it was going to do without anything being visible about block files.
0.14.0 is marked insecure because of
CVE-2018-17144-- just a software bug. Nothing to be excited about there.
The reason the dates on old file on that page is because old versions didn't used to get left up at all (due to space usage reasons). Later the old versions were put online. The old files are all unchanged e.g.
[gmaxwell@bean tmp]$ wget https://bitcoincore.org/bin/bitcoin-core-0.10.0/bitcoin-0.10.0.tar.gz
--2020-05-09 00:52:55-- https://bitcoincore.org/bin/bitcoin-core-0.10.0/bitcoin-0.10.0.tar.gz
Resolving bitcoincore.org (bitcoincore.org)... 107.191.99.5, 198.251.83.116
Connecting to bitcoincore.org (bitcoincore.org)|107.191.99.5|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 4152163 (4.0M) [application/octet-stream]
Saving to: bitcoin-0.10.0.tar.gz
bitcoin-0.10.0.tar.gz 100%[=====================================================================================>] 3.96M 3.50MB/s in 1.1s
2020-05-09 00:52:57 (3.50 MB/s) - bitcoin-0.10.0.tar.gz saved [4152163/4152163]
[gmaxwell@bean tmp]$ sha256sum bitcoin-0.10.0.tar.gz
a516cf6d9f58a117607148405334b35d3178df1ba1c59229609d2bcd08d30624 bitcoin-0.10.0.tar.gz
Which matches the hashes you can find from peoples
posts at the time.
When you run old versions (but new enough to know about
BIP9) they will warn if blocks have different version numbers than they expect. If you're just making transactions these warnings are
completely harmless, there there so that you know not to mine with that version (you might waste your time producing an invalid block), or if you are accepting transactions you should wait for more confirmations to be confident that they're final. The reason for this is that over time Bitcoin gains new functionality in a way that is completely backwards compatible, can't risk your existing funds, and won't stop existing wallets from working.
In short, there is nothing at all of interest here.
And if "Euro Chems" is saying otherwise, then perhaps they've been using some of their own "chems".