Why don't currency years line up with the coins years?

For example https://en.numista.com/catalogue/index.php?e=poland_section&r=&ct=coin&tb=y&tc=y&tn=y&tp=y&tt=y&cat=y&ru=&ca=3&no=&v=50&d=&i=&a=1923&dg=&m=&f=&t=&w=&u=&g=&se=&c=&wi=&sw=
says the 2nd polish zloty started in 1924 but there are coins from the previous year under that currency I have noticed this alot.

You do realize that coins are produced at a mint & paper money is produced at a separate printing facility? They have completely different (& unique) production demands/processes. Coins are given a new year ever single year (with some years occasionally skipped) whereas banknotes have a series design printed every X ___ # of years since new designs are expensive (& requires training & even sometimes re-tooling cash machines). Some banknotes have the year of the issue, others don't while other nations may have the year printed as an imprint (smaller printing on the bottom border).

Some nations have their banknotes printed at a private printers and then shipped (in uncut reams) to the central bank where the serial # & signature or some type of overprint (last steps) before being cut & released (issued to bank distributing centres).

Perhaps just a few reasons that people will seldom see coin/banknote series released simultaneously (or lining up).

He meant why doesn't the coin currency type match the years the coin was minted. In his example, a Poland 50 Groszy is under Second złoty (1924-1949) but was minted in in 1923.

The coins were minted in 1923, but the new currency was probably introduced only in 1924.

Another vivid example can be Ukrainian kopiykas. They were minted in 1992, 1993, 1994, 1995, but the currency was officially introduced only on September 2, 1996.

Also a prominent example is the euro was introduced in 2002 France, the Netherlands and others started the production in 1999. Some countries print the actual year of production many the year of planned issue.

Cita: "rsirian1"​He meant why doesn't the coin currency type match the years the coin was minted. In his example, a Poland 50 Groszy is under Second złoty (1924-1949) but was minted in in 1923.
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​Well, I still stand by may answer. The production process of coins (& notes) takes time.