This is where it’s important to remember who exactly is writing the laws for union recognition. Many countries have laws that nominally support the formation of unions but moreso exist to reduce union support or funnel unions into polite, legal activity.
The math is not right. Percentages don’t multiply like that.
A change from 0.25 to 7.25 over 71 years means an annual increase of about 5%. That 5% annual change, starting with $7.25 15 years ago, would take us to around $15 today.