Find First/Last Value In Row & Return Corresponding Description Above/Below

I'm trying to find

1) the last and

2) first values in a time series of data in which the the data points are scattered all over the place

AND I'd also like to

3) get the corresponding year ( Heading name) for both the

3.1) last and the

3.2) first data point

I've found solutions for all but 3.2. Thus the question remains:

How could I lookup the heading description for the first value on a row?

example:

row #; lookup; year1; year2; year3; year4;
1; year3; ; ; 23; ;
2; year2; ; 21; ; 53;
3; year1; 12; ; 45; 2;

In case it helps anyone looking for same information or providing help to solve my problem 3.2 the other solutions I've found are:

1) lookup last value in row

i) Find Last Number In Row & Return Heading
=LOOKUP(9.99999999999999E+307,R5:AI5)
... also an additional VB solution

ii) Find Last Number In Row & Return Heading
=INDEX(M12:M500;MATCH(9.99999999999999E+307;M12:M500))
... page also includes solution for 2), below

iii) Find Last Number In Row & Return Heading
... 2 VB solutions

2) Lookup first value in row
Find Last Number In Row & Return Heading

=INDEX(M12:500,MATCH(TRUE,INDEX(M12:M500<>0,0,0),0))
... page also includes solution for 1), above

and

3) Lookup heading of last populated cell in row
Find Last Number In Row & Return Heading

=LOOKUP(2,1/(I9:CN9<>""),I$5:CN$5)

4) Could I e.g. modify the above to lookup the year of first value?