Bash Command (History) Number In PS1

I have concluded that it is not possible to append the new commands directly and at the same time to remove any duplicates. So my solution is to run the following command ones in a while. or to put it in my crontab.

tac $HOME/.bash_history | awk '!seen[$0]++' | tac > $HOME/.hist_Temp 
mv $HOME/.hist_Temp $HOME/.bash_history

The above command will keep the last occurrence of a command and remove every other repetitions above it from the history file without messing up the order.

Bash's command number is for display only.

First, some background from bashref:

The command number and the history number are usually different: the history number of a command is its position in the history list, which may include commands restored from the history file (*note Bash History Facilities::), while the command number is the position in the sequence of commands executed during the current shell session.

Diving through the source, in parse.y we see that '\#' resolves to the global static variable current_command_number:

case '#':                                                                     
  n = current_command_number;                                                 
  /* If we have already incremented current_command_number (PS4,              
 ${var@P}), compensate */                                                     
  if (orig_string != ps0_prompt && orig_string != ps1_prompt && orig_string != ps2_prompt)
n--;                                                                          
  temp = itos (n);                                                            
  goto add_string;                                                            

which only has one other use: in eval.c, it's incremented upon running a command:

# ...
current_command_number++;                                                  

executing = 1;                                                             
stdin_redir = 0;                                                           

execute_command (current_command);                                         

All that's kept is a number, not the actual command or even the equivalent history number. So, upon execution of each command, bash forgets what command associated with what command number, rendering the command number unusable for anything other than display and scroll reference.