Show original vacancies is not intuitive (numbers in brackets)

[lunaflight]

Describe the problem
The show original vacancies button is not self-explanatory and sticks out like a sore thumb.
The idea of this button is that in the vacancy report, the number of available seats for a course seems to differ from the actual available seats for a course after demand allocation happens. See CS2103T - it is always forecasted to be 18 seats but always promoted to 20 seats after the fact.
This needs to be more intuitive to a user than just an unexplained parenthesis with a togglable that nobody (citation needed) presses.

Describe the feature
We could potentially make ↑ ↓ arrows beside the number to show if it is higher or lower than the actual vacancy forecast. We could also then potentially remove the togglable / make the togglable off by default.
Users are probably not very interested in the actual discrepancy unless it is very high, so arrows can be good to reduce visual clutter.
We could use multiple arrows like ↑↑ ↓↓ if the change is very large (say more than 25%?)