Formula to create concatenated size data for groups of products

[cwhyte1984]

I have the following data:

Product Name	Size	All sizes
Maxomorra Bikini Bottom Rainbow	Age 9-10 Yrs
Maxomorra Bikini Bottom Rainbow	Age 11-12 Yrs
Maxomorra Bikini Top Rainbow	Age 2-3 Yrs
Maxomorra Bikini Top Rainbow	Age 3-4 Yrs
Maxomorra Body Long Sleeve Solid Blue Sky	Age 6-12 Mths
Maxomorra Body Long Sleeve Solid Pink Blossom	Age 0-3 Mths
Maxomorra Body Long Sleeve Solid Pink Blossom	Age 3-6 Mths
Maxomorra Body Long Sleeve Solid Pink Blossom	Age 6-12 Mths
Maxomorra Body Long Sleeve Solid Yellow Sun	Age 3-6 Mths
Maxomorra Body Long Sleeve Solid Yellow Sun	Age 6-12 Mths
Maxomorra Body Long Sleeve Tales Fairy	Age 3-6 Mths
Maxomorra Body Long Sleeve Tales Fairy	Age 6-12 Mths
Maxomorra Body Long Sleeve Tales Unicorn	Age 6-12 Mths
Maxomorra Body Long Sleeve Tales Unicorn	Age 12-24 Mths
Maxomorra Body Short Sleeve Solid Blue Sky	Age 0-3 Mths
Maxomorra Body Short Sleeve Solid Blue Sky	Age 3-6 Mths

I need a formula to create a list of sizes for all of the products available in that style in column 'All Sizes' . I have spent some time with ChatGPT working on it but i continually get circular reference errors. As an example of the data required here is what it should look like:

Product Name	Size	All sizes
Maxomorra Bikini Bottom Rainbow	Age 9-10 Yrs	Age 9-10 Yrs,Age 11-12 Yrs
Maxomorra Bikini Bottom Rainbow	Age 11-12 Yrs	Age 9-10 Yrs,Age 11-12 Yrs
Maxomorra Bikini Top Rainbow	Age 2-3 Yrs	Age 2-3 Yrs, Age 3-4 Yrs
Maxomorra Bikini Top Rainbow	Age 3-4 Yrs	Age 2-3 Yrs, Age 3-4 Yrs
Maxomorra Body Long Sleeve Solid Blue Sky	Age 6-12 Mths	Age 6-12 Mths
Maxomorra Body Long Sleeve Solid Pink Blossom	Age 0-3 Mths	Age 0-3 Mths, Age 3-6 Mths, Age 6-12 Mths
Maxomorra Body Long Sleeve Solid Pink Blossom	Age 3-6 Mths	Age 0-3 Mths, Age 3-6 Mths, Age 6-12 Mths
Maxomorra Body Long Sleeve Solid Pink Blossom	Age 6-12 Mths	Age 0-3 Mths, Age 3-6 Mths, Age 6-12 Mths
Maxomorra Body Long Sleeve Solid Yellow Sun	Age 3-6 Mths
Maxomorra Body Long Sleeve Solid Yellow Sun	Age 6-12 Mths
Maxomorra Body Long Sleeve Tales Fairy	Age 3-6 Mths
Maxomorra Body Long Sleeve Tales Fairy	Age 6-12 Mths
Maxomorra Body Long Sleeve Tales Unicorn	Age 6-12 Mths
Maxomorra Body Long Sleeve Tales Unicorn	Age 12-24 Mths
Maxomorra Body Short Sleeve Solid Blue Sky	Age 0-3 Mths
Maxomorra Body Short Sleeve Solid Blue Sky	Age 3-6 Mths

And so on. There are 1000's of lines of products thus the need to do this.

Here is the example of the ChatGPT code which isnt far away from what I think i require.

=IF(A1<>A2,B1,IF(COUNTIFS(A:A,A1,D:D,"")=0,B1,IF(COUNTIF(A:A,A1)>1,INDEX(D:D,MATCH(A1,A:A,0))&","&B1,B1)))

Help greatly appreciated.

[#2]

@cwhyte1984 

You can try Power Query. In the attached file you can add data in the blue dynamic table. Then you can click in any cell of the green table and right-click with the mouse and select refresh in order to update the green result table.

[#3]

@OliverScheurich hi there.  Thanks for the reply. I am trying to use basic formulae to do this as this file is generated from another excel with various pieces of product data. Ideally I would be able to just input the size data from the original manufacturer supplied file and then copy the formula down without the need for further manipulation. 
Once this file is created it is used as a .csv to upload product data to site. 

[#4]

@cwhyte1984 

=IFERROR(INDEX(Tabelle2!$B$2:$B$21,SMALL(IF(Tabelle2!$A$2:$A$21=Tabelle2!$A2,ROW(Tabelle2!$A$2:$A$21)),COLUMN(A$1))-1),"")

You are welcome. You can try this formula which works in Excel 2013. Enter the formula with ctrl+shift+enter in order to confirm it as an arrayformula. The formula is filled down and to the right in the attached samplefile.