Hopefully this will make things a little clearer, here is the example I linked in text:
[TABLE="class: grid, width: 500, align: center"]
<tbody>[TR]
[TD][TABLE="width: 177"]
<tbody>[TR]
[TD="class: xl66, width: 177"]QUOTE REFERENCE[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl66, width: 155"]SUPPLIER[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 107"]
<tbody>[TR]
[TD="class: xl66, width: 107"]PURCHASING ORDER NUMBER[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 131"]
<tbody>[TR]
[TD="class: xl66, width: 131"]DATE ORDERED FROM SUPPLIER[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 237"]
<tbody>[TR]
[TD="class: xl66, width: 237"]PURCHASE ORDER GENERATOR[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
[TR]
[TD]
[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl65, width: 155"]AMAZON[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 107"]
<tbody>[TR]
[TD="class: xl65, width: 107"]1000[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 131"]
<tbody>[TR]
[TD="class: xl65, width: 131"]20/08/2015[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 237"]
<tbody>[TR]
[TD="class: xl65, width: 237"]PO-AMAZON-200815[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
[TR]
[TD]
[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl65, width: 155"]AMAZON[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 107"]
<tbody>[TR]
[TD="class: xl65, width: 107"]1000[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 131"]
<tbody>[TR]
[TD="class: xl65, width: 131"]20/08/2015[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 237"]
<tbody>[TR]
[TD="class: xl65, width: 237"]PO-AMAZON-200815[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
[TR]
[TD]
[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl65, width: 155"]EBAY[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 107"]
<tbody>[TR]
[TD="class: xl65, width: 107"]1001[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD]20/08/2015[/TD]
[TD][TABLE="width: 237"]
<tbody>[TR]
[TD="class: xl65, width: 237"]PO-EBAY-200815[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
[TR]
[TD]1075[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl65, width: 155"]EBAY[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD]1002
[/TD]
[TD]27/08/2015[/TD]
[TD][TABLE="width: 237"]
<tbody>[TR]
[TD="class: xl65, width: 237"]PO-EBAY-270715[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
[TR]
[TD][TABLE="width: 177"]
<tbody>[TR]
[TD="class: xl65, width: 177"]
[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl65, width: 155"]EBAY[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD]1001[/TD]
[TD]20/08/2015[/TD]
[TD][TABLE="width: 237"]
<tbody>[TR]
[TD="class: xl65, width: 237"]PO-EBAY-200815[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
[TR]
[TD]
[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl65, width: 155"]TOOLWORKS[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD]1003[/TD]
[TD]20/08/2015[/TD]
[TD][TABLE="width: 237"]
<tbody>[TR]
[TD="class: xl65, width: 237"]PO-TOOLWORKS-200815[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
[TR]
[TD]
[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl65, width: 155"]FIREBOLTS[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD]
[/TD]
[TD]
[/TD]
[TD]
[/TD]
[/TR]
[TR]
[TD]
[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl65, width: 155"]BUTLINS[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD]1004[/TD]
[TD]21/08/2015[/TD]
[TD][TABLE="width: 237"]
<tbody>[TR]
[TD="class: xl65, width: 237"]PO-BUTLINS-210815[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
[TR]
[TD]
[/TD]
[TD][TABLE="width: 155"]
<tbody>[TR]
[TD="class: xl65, width: 155"]AMAZON[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[TD]1005[/TD]
[TD]28/08/2015[/TD]
[TD][TABLE="width: 237"]
<tbody>[TR]
[TD="class: xl65, width: 237"]PO-AMAZON-280815[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
</tbody>[/TABLE]
Columns A, B & D are manual.
C starts with manual number 1000, then column below is formula:=IF(COUNTIF($E$2:$E$3,$E3)=1,IF($A3="",MAX(IF($C$2:$C2<40000,$C$2:$C2))+1,MAX(IF($D$2:$D2&$D4:$D1000<$D3,$C$2:$C2&$C4:$C1000))+1),INDEX($C$2:$C2,MATCH($E3,$E$2:$E2,0)))
Column E is formula: =IF(D2="","",CONCATENATE("PO-",B2,"-",TEXT(D2,"DDMMYY")))