The early December 2013 network snapshots, i.e. with over 100k nodes, are not valid as the crawler at that time took several hours just to complete one full network snapshot and it includes all nodes from addr responses which can be faked or likely stale. Those snapshots were linked to from getaddr.bitnodes.io/SNAPSHOT_NUMBER/ which have been removed since.
With the new crawler released in late Dec 2013, the crawl time was brought down significantly down to sub 5 minutes with considerably good churn rate. I use the churn rate to measure how good a network snapshot is. A value of 0 implies the network snapshot was taken instantly but of course that's not possible. At the moment, we are seeing a typical churn rate of 30+:
https://getaddr.bitnodes.io/nodes/That's a definitive answer.
Thanks for helping resolve the issue.
The above explanation would have provide noticeable results quickly, however it does not account the observable drop in nodes over time.
https://bitinfocharts.com/comparison/nodes-btc-ltc.html#logYou can see that there are serious technology implications and mining adoption pertaining to full BTC nodes and the migration from GPU mining to ASIC.
P.S. As to your question "Q3. Is is possible to ever see that number again?"
Introducing incentive by granting % of transaction fee's to the node that relays may help.