2012600 - Are there differences between sp_primarykey and creating a primary key constraint in ASE?

• Is there a difference between defining a primary key with sp_helpkey and creating a primary key constraint in ASE?
• Why is there conflicting information  between results of sp_helpkey and sp_helpconstraint?
• Is there a column limitation when defining a primary key?

SAP Adaptive Server Enterprise (ASE) All Versions

KBA , BC-SYB-ASE , Sybase ASE Database Platform (non Business Suite) , How To