Indeed, useful as "Reference URL" here:

Good idea. And you and I have exchanged on the need for some of the chemicals to be collapsed together too so the curation effort would affect those numbers. If you want me to do anything re looking for duplicates with mapping exercise let me know. I will dedicate a little time every day.

On that note we could add the number of compounds by unique InChIKeys and also the numbers by unique first block to collapse down the (stereo)isomers ... would be an interesting statistic to have.

Implemented with 50fb7ca and rolled out on the dev server server. I added 3 numbers: Unique Spectra corresponds to the the total number of accessions, Unique Compounds is the count of unique InChI-keys and Unique Isomers is the count of unique first blocks of InChI-keys. I have not added a section of records without InChI-keys which is around 3000 atm. With some work it will come down to less than 900. This can be closed with the next rollout of the official MassBank server.

I updated the entry in Wikidata: https://www.wikidata.org/wiki/Property:P6689

So ... this appears only on the msbi.ipb-halle record index still it seems, but is there an issue with the numbers? More isomers than compounds? What do we mean with "isomer" vs "compound"? Can we name them more accurately?
Unique Compounds (with stereoisomers)
Unique Compounds (without stereosiomers) or Unique Compounds (same skeleton)?
(better ideas welcome, I realise there is space limitation)

https://msbi.ipb-halle.de/MassBank/RecordIndex

yep, should he solved next weekend. I am relactant to change the sever in the week because of the service availability. And we have still some issues with the deployment...

So ... this appears only on the msbi.ipb-halle record index still it seems

Yes, thats true but @tsufz is working on that issue. 👍

, but is there an issue with the numbers? More isomers than compounds? What do we mean with "isomer" vs "compound"? Can we name them more accurately?

I implemented my understanding of the topic:
Lets have two Spectra, one from L-Alanin and one from D-Alanin. Than we have one unique compound (Alanin) and two unique Isomers. Do you find this logic irritating? Should we name it differently? Should we count different things?

Well the problem is that isomers are defined on many different levels, and most would count a unique stereoisomer as a unique compound - hence the confusion.
I would propose something like Compounds (with stereoisomers) and Compounds (without stereoisomers) to clarify more exactly what you mean. Most users will not really know the InChIKey first block assumption (although many do in the meantime).

Interesting ontological discussion :)

So, the IUPAC Goldbook does not have a definition of chemical compound or compound, but Wikipedia defines a compound as follows: Chemical compounds have a unique and defined chemical structure held together in a defined spatial arrangement by chemical bonds.