Can I use a single letter or symbol to represent "actual" in a table? I have a chart that displays numbers for 2017, 2018, 2019 and 2020, but the 2020 numbers are based on projections - I want to display the "actual" value on the data label next to the projected number - is there a single symbol or letter that I could use for this? Something so that it looks like:
3235 (my projected number)
a = 2887 (my actual number)
 A: If there is a symbol then it is likely not very commonly known. So in any case you have to explain it somewhere what the symbol means and it might confuse your readers.
However, if you have to plot multiple tables then it might be useful to abbreviate notation.
A possible way could be to use markers like an asterix $^*$ or other symbol that indicates a footnote.
For instance a table could look like
2017       3011
2018       2987
2019       3132
2020*      3235 
2020**     2887

*Projected figure  **Current actual figure 
Or like
2017       3011
2018       2987
2019       3132
2020*      3235 (2887)

 *projected figure (current actual figure) 
I often see tables with only the projected figure (and some marker and footnote to explain it is projected) but I admire your attempt to also show the current figure. An alternative could be
Year       Number of statisticians going crazy
2017       3011
2018       2987
2019       3132
2020*      3235

 *projected figure based on current 2887 statisticians
