Yes, I understand you are using MXROAD.
However, MXROAD contains a range of OpenRoads tools (under the Civil Tools task) which create 'Civil Data' - separate from 'normal' MX models and strings. Any OpenRoads civil data created in SS2/3 can be opened in SS4 - but it will not be backward compatible.
Standard MX models and strings are not affected by a move to SS4.
However, MXROAD contains a range of OpenRoads tools (under the Civil Tools task) which create 'Civil Data' - separate from 'normal' MX models and strings. Any OpenRoads civil data created in SS2/3 can be opened in SS4 - but it will not be backward compatible.
Standard MX models and strings are not affected by a move to SS4.